The most powerful civilization in South America before the arrival of Europeans was the mighty Inca empire, which ruled much of the continent's Pacific coast from their home in the Peru highlands. And it's all thanks to copious llama crap.

The Inca civilization reached its peak in the 14th and 15th centuries, just before the arrival of Spanish conquistadors. They ruled over an empire that at is height covered some 775,000 square miles, encompassing large parts of what is now Ecuador, Peru, Bolivia, Colombia, Chile, and Argentina. So where does the llama dung enter the picture? For that, we need to go back about 2,000 years before the Inca Empire.

Maize (otherwise known as corn) has been the staple crop of most of South America, and figuring out how to grow it is what has allowed various groups to move away from being hunter-gatherers and to embrace agriculture. In turn, mastering how best to cultivate the crop allowed groups to expand their cultural imprint and ultimately build up the resources necessary to wage war and forge empires.

Now, the Peruvian highlands do not seem like the most obvious place for an agricultural revolution, certainly not for a civilization as powerful and expansive as the Inca. And yet 2,700 years ago, the crop suddenly became dominant in regions some two miles above sea level, as analysis of the archaeological record reveals the ancient Peruvians switched from eating wild foods to eating maize.

The archaeological record also reveals a sudden upswing in the number of manure-eating oribatid mites, which in turn implies that there were tons more big animals pooping in the highlands. That means llamas were creating tons of natural fertilizer, and that was the real engine of the crop's success in the highlands. Alex Chepstow-Lusty of the French Institute of Andean Studies, who led this new research, explains why all the llama crap was so important:

"The widespread shift to agriculture and societal development was only possible with this extra ingredient – organic fertilisers on a vast scale."

So then, thanks to these ancient llamas - and most likely a briefly warmer climate, but that's way less interesting because it doesn't involve poop - the peoples of the Andean highlands were able to become accomplished agriculturalists. And because the maize crop can be stored for long periods and can be traded easily, it was the ideal crop to drive the eventual formation of the Inca empire some two millenniums later.